#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>

double CancelFee(double price)
{
	price = price * 0.05;
	double tmp = (int)price;
	price = price - (int)price;
	if (price < 0.25)
		return tmp;
	else if (price > 0.25 && price < 0.75)
		return tmp + 0.5;
	else
		return tmp + 1;
}

int main()
{
	double p;
	double ret;
	scanf("%lf", &p);
	ret = CancelFee(p);
	printf("%.1f", ret);
}